Young playwrights turning out promising new works. Jonathan Marc Sherman has an outstanding entry

The seventh annual Young Playwrights Festival gains a familiar touch of symbolism from its locale - the Playwrights Horizons Mainstage on West 42nd Street, where the promising new works are being premi`ered. Helping open up new horizons for the under-20s authors are their professional advisers and directors and the Foundation of the Dramatists Guild, which sponsors the forward-looking festival. The three works, chosen from 612 submissions, speak well and clearly for this new generation of writers. The most ambitious and accomplished of the latest collection is Jonathan Marc Sherman's ``Women and Wallace,'' a touchingly funny account of how young Wallace Kirkman (Josh Hamilton) gradually comes to terms with the trauma of his mother's suicide when he was six years old. The women in question begin with the caring Mother herself (Mary Joy), who remains a background figure throughout the proceedings. Among others, Wallace's ordeal also passingly involves a psychiatrist (Debra Monk), his compassionate but clear-sighted grandmother (Joan Copeland), and in particular the fellow student (Joanna Going), whose blend of love and self-respect jolts Wallace into the maturity that frees him.

``Women and Wallace'' has been sensitively staged by Don Scardino (with Albert Innaurato as adviser). The result on the Playwrights Horizons stage is a theater piece delicately balanced between the comic and the poignant. Mr. Hamilton conveys Wallace's maturing process with an intuitive sensibility that comprehends the shattering dismay, callow uncertainties, and emotional coming-of-age. The actor is aided by an impressive surrounding cast.

Robert Kerr's ``And the Air Didn't Answer,'' directed by Christopher Durang with Morgan Jenness as adviser, probes a youthful crisis of faith. As Dan Wilson (Robert Sean Leonard) is preparing his talk for a Roman Catholic youth group, he suddenly discovers that he no longer believes in what he is saying. Neither his mother (Miss Monk), his girlfriend (Jill Tasker), the local priest (Richard Council), nor the local scoutmaster (Mr. Council again) proves a match for what Dan regards as his atheism.

Mr. Kerr presents the lad's crisis in comic and frequently fantastic terms. Confined to his room by a distraught mother, Dan not only fantasizes a sightseer's glimpse of the inferno with Dante as guide, but envisages a very white-bearded anthropomorphic God, whose pronouncements don't help. Nor does some woodsy communing in the company of a Transcendental Meditationist schoolmate (Erica Gimpel) prove particularly enlightening. ``And the Air Didn't Answer'' leaves poor Dan just about where it found him - up in the air. Meanwhile, young Kerr demonstrates his flair for comedy, fantasy, and the addressing of sharp questions.

With Mr. Leonard's appealing performance as the bemused Dan and lively work by all concerned, Mr. Durang has staged the play deftly and with the fellow feeling of one whose own protestations surfaced in ``Sister Mary Ignatius Explains It All for You.''

Eric Ziegenhagen's ``Seniority,'' directed by Lisa Peterson, is an amusing conversation piece in which high school senior Debbie (Bellina Logan) finds herself confronting the challenges of her younger, prettier, and more sophisticated sister Fiona (Allison Dean). Debbie also discovers how she unintentionally discouraged the attentions of Ian (Jihmi Kennedy), a fellow student Fiona has appropriated.

``Seniority'' (with Alfred Uhry as adviser) applies a light touch to the problems of sibling rivalry. Miss Peterson has staged a performance that responds to the emotional nuances and crosscurrents of a familiar situation.

The common denominator of this year's festival is the gift for comedy displayed by the trio of young playwrights - not to mention a maturity of viewpoint that sometimes approaches precocity. As usual, the plays have received artistically well appointed productions, with simple but attractive sets by Allen Moyer, costumes by Jess Goldstein, and lighting by Nancy Schertler. The festival continues through Oct. 31 and will include several staged readings of Kevin Corrigan's ``The Boiler Room.''